The prior art patents enumerated above disclose engines or rotary machines which are of a type, by way of example, those machines having two or more intersecting rotors.
As disclosed in such patents, the piston faces exposed to the combustion gases of the power stroke are subjected to heat for the full length of the power stroke. By way of contrast, the inner hub surfaces of the rotor cavity of such engines is exposed to the heat of combustion for a varying length of time along its surface, i.e., a longer period of time near the piston face diminishing to a short period of time near the trailing face of the cavity, and the trailing face of the cavity is scarcely exposed to the heat of combustion as the exhaust cycle has started at about the time the trailing face is exposed to the combustion gases of the power stroke. In addition to the unequal distribution of heat above described on the rotor performing a power stroke, the adjacent rotor, the side surface of which is used as a reactive surface of the first rotor power stroke and then is subjected to the heating of combustion on one side surface only. Concurrently, the opposite side of the same lobe of that respective rotor is subjected to the heat of compression for the next following power cycle. Thus one side of each lobe of each rotor is exposed to the heat of combustion while the other side of the same lobe is concurrently exposed to the heat of a compression stroke at a much lower level.
It is thus apparent that in the cycling of the engine through intake, compression, combustion and exhaust, that various surfaces of the interacting rotors are subjected to wide extremes of temperature at any given point in time.
In addition, while the outer housing, block, or stator of this engine may be cooled by the various conventional means disclosed in the foregoing patents, such as means comprising cored passages for liquid cooling, or heat radiating fins cooled by the passage of air over them to reject heat, the rotors of the prior art engines are not subject to cooling in the same sense that is accomplished in a conventional reciprocating piston engine by conduction, either direct or through oil films to the housing walls.
One of the desirable features of the prior art engines is that lubricating oil is not exposed to the through flow or power cycle of the engine, or in the compressor species as the case may be.
It is possible to cool the rotors of such prior art machines by circulating a coolant liquid through rotating seals and the shafting of the rotors and through the passageways in the interiors of the rotors and thus reject heat to the ambient surrounding area as in the case of the housing functioning as casing cooling. However, this is undesirable from the standpoint of engine efficiency and fuel economy. Heat thus rejected is lost to the cycle or the net shaft power generated by the engine for a given amount of fuel.
It will be appreciated that the prior art as represented by the foregoing patents includes engines which are basically normally aspirated engines wherein the evacuation of the rotor chambers causes a negative pressure which induces air to flow into the rotor chambers but which does not provide for supercharging of such engines. It being understood, however, that a shaft driven compressor externally of such prior art engines might be used to provide for supercharging of the rotor chambers thereof such as has been used in connection with many piston engines.